Vacuum discharge vessel



March 22, 193.

W. DALLENBACH VACUUM DISCHARGE VESSEL Filed Aug. 13, 1934 Patented Mar.22, 1938 UNITED STATES PATENT oFFicE many, assignor to N.

V. Machinerieen-en Apparaten Fabrieken Meat, Utrecht, NetherlandsApplication August 13 1934., Serial No. 739,678

In Germany June 22, 1934 4 Claims.

-5 vide between the anode and cathode, directly before the anode, apartition dividing the inner space of the discharge vessel into asmaller space adjoining the anode surface and a larger one. Thepartition possesses one or several small apertures equal in size to themean free length of path of the particles of the gas or vapor content,and means are further provided for operating the tube at a currentintensity which, owing to the constriction of the discharge by thediaphragm in the space adjoining the active anode surface, involves adecrease in the number of positive ions, so that a drop in voltageincreasing with the current intensity will take place in that space.

A further object is to limit the distance from the partition to theanode to a maximum equal to a few lengths of path of electrons in thegas or vapor.

Another object is to construct the apertures in the form of elongatedchannels.

Another object is to produce the partition from metallic material and toconnect it to the anode by means. of aresistance.

A further object is to employ control electrodes for influencing thecurrent passing through the opening of the partition.

Still anotherv object is to connect in series with the discharge tube aresistance or choker dimensioned so that the tube will carry out slowautomatic oscillations similar to those of a flash lamp.

Further details will become apparent from the specification and theaccompanying drawing, in which Figure 1 is a diagram of a characteristicof a discharge tube according to the invention; Fig. 2 shows theconstruction of such a tube by means of a mercury cathode and anauxiliary ignition electrode; Fig.3 shows a cathode ray tube withdeflecting electrodes; Fig. 4 shows a tube provided with two anodeswhich alternately may receive the cathode ray by means of controlelectrodes; Fig. 5 shows a tube, in which the partition made of metallicmaterial is connected to the anode by a resistance; Fig. 6 shows ananode with a partition, in which a number of apertures having the formof small channels are provided;

and Fig. 7 shows a diagram of connections for ob-- taining slowfiashlike oscillations.

In vacuum discharge tubes having a rarefied gas or vapor filling it canbe observed that the drop in voltage will decrease at first when thecurrent intensity increases from low values and increase again at veryhigh intensities. This increase is particularly marked and takes placeat still permissible current intensities if the anode is enclosed in achamber communicating with the remainder of the inner space of thedischarge vessel only by means of a small diaphragmlike opening. .Thesmaller the contents of this chamber and the narrower the communicatingopening between the chamber and the rest of the tube space, the steeperwill be the current-voltage characteristic beyond a certain current loadand the smaller the current intensity at which the characteristic willbegin to rise again.

Fig. 1 shows the current-voltage diagram of such a gas discharge tube. Amore accurate examination shows. that in following the voltagecharacteristic up to the point where it begins to ascend a branch willbe reached which rises in vertical direction. This means that thecurrent J reaches saturation, the saturating current intensitydependingupon the gas pressure within the tube.

In Fig. 2, a tube of this kind is shown. A is the anode; B, thediaphragm surrounding the anode; and K a cathode. of the mercury or hottype. In case of a mercury cathode, an exciter anode E is, as a rule,required to maintain the exciter arc towards the cathode K, though theexciter anode becomes superfluous if enough current is takenfrom thecathode.

The saturating current intensity for the cur, rent passing from thecathode to the anode is brought about as follows:

In the diaphragm opening a so-called striction cathode is formed whichall electrons coming from the cathode have to pass. At the point oflocation of this cathode a fixed relation exists between the electroncurrent passing from the cathode to the anode and the positive stream ofions passing in reversed direction from the anode to the cathode. Theratio of the electron current to the ionic current must be Jr m m beingthe mass of positive ions and me the mass of electrons. The value formercury vapor will therefore be 605, i. e., the electron current passingfrom the cathode to the anode is 605 times greater than the oppositelydirected ionic current. As the chamber formed by B tightly shuts oii theanode from the remaining portion of the vacuum vessel, the positive ionsprojected by the positive ionic current Jp through the diaphragm openingfrom the chamber into the discharge space C must necessarily be suppliedlater on in some way, which is effected by the diffusion of neutralmercury atoms from the discharge tube through the diaphragm opening intothe inside of the chamber. This diifusion is due to the temperaturemotion of the mercury atoms. The number of neutral gas particles whichdiffuse at low gas pressure through a diaphragm opening is known to bedependent solely on the number of particles per unit of Volume and thetemperature, i. e., the intensity of motion of these particles. As longas the density of the gas, particularly the density of the mercuryvapor, and the temperature of the gas in front of the diaphragm openingremain unchanged, the inflow of particles through the diaphragm openinginto the inside of the anode chamber will therefore be constant and thedischarging current intensity fixed. When the saturating currentintensity has therefore been reached, 1. e., as soon as the depletion ofions inside the anode chamber takes place and the point P has beenreached in the characteristic according to Fig. 1, only the inflowinggas particles will be available for covering the positive ionic current.As this positive ionic current intensity, according to the equationstated, has a fixed relation to the electron current, the saturationcharacter that is actually observed will follow therefrom.

The electron current passing through the stric tion cathode formed inthe diaphragm opening runs through the space towards the anode as aregular ray. The striction cathode acts there fore in the hollow space Eas a novel type of cathode (plasma cathode), as it is fed by theirregularly moving electrons, the so-called plasma, in the space C. Inview of the extraordinarily high current densities which are possible ina gas discharge, current densities can be attained by means of thisplasma cathode, which considerably exceed the densities of the usual hotcathodes. It thus becomes possible to produce with this plasma cathodein the chamber B a cathode ray of much higher density than could beattained with, say, a hot cathode.

The possibilities of application of this novel cathode are quite varied.For example, it may be used as cathode ray oscillograph by employing afluorescent screen or a window of metal foil with a fluorescent screenarranged behind it instead of the anode A. Such an arrangement is shownin Fig. 3. O is the window; D represents the deflecting electrodes and Lthe fluorescent screen. It is further possible to produceextraordinarily intense X-rays with this arrangement, and the canal raysformed by the ions passing from the anode through the diaphragm may beused also in the ordinary way.

For controlling the electronic ray electrodes D may be provided insidethe chamber B to produce a transverse field, as indicated in Fig. 4.

To obtain a modulation by means of the controlled electronic current theanode is preferably divided into the two parts A1 and A2 (Fig. i) which,according to the voltage applied, take up at the auxiliary electrodes Dthe electron current in whole or in part, or not at all.

Fig. 4 also shows how such a discharge vessel may be used ascounter-contact amplifier in the manner usual in electron tubes. If theauxiliary electrodes D are supplied with control voltages by the line S,they can be taken oii amplified at the outlet A.

If the input and output conductors are connected to corresponding polesand constructed as a resonance circuit, the discharge vessel willfunction as counter-contact generator whose oscillation frequency may bevaried within wide limits.

The discharge vessel described may further be used for limiting current.As indicated in the characteristic of Fig. 1, the current intensitycannot increase beyond the value at point P as long as the gas pressuremaintains a certain value, and the tube can thus be employed assteadying resistance in front of apparatus which, for example, arealways to be operated at a certain current intensity regardless of thefeeding voltage. For this purpose, hot cathode tubes are known, but incontrast with the latter considerable current intensities can be keptconstant in this manner, according to the invention, by simple means andat low power input. As cathode K for the discharge and the formation ofthe plasma cathode proper in the opening F of the diaphragm B a hot or amercury cathode with or without the exciter anode E may be employed inthe usual way. If a mercury cathode is chosen, it is desirable to keepthe mercury vapor pressure constant near the diaphragm opening, whichcan be done for instance by disposing the tube in a thermostat.

Another possibility consists in filling the tube with a rare gas of suchhigh pressure that, in comparison, the mercury vapor pressure is of noimportance. The higher the gas pressure chosen, the smaller must be thediaphragm opening in view of the saturation current intensity involved.

Further use can be made of the arrangement if gas discharge lamps are tobe operated connected to a supply network without a series re sistanceor choke. The omission of the series resistances and chokes saves theotherwise required reactive power and thus increases efiioiency. Thesetubes permitting the construction of small luminous tubes connecteddirectly to the network, can be employed with special advantage inlighting.

If in this way any impedance in series with the electric dischargevessel is to be avoided and the latter to be connected directly to thenetwork, it is necessary that, compared with the partial voltage dropsof the gas discharge decreasing with increasing current intensity, thedrop in voltage increases to such an extent that the entire drop involtage between the anode and cathode increases with the currentintensity.

The invention is thus of special importance for all electric dischargevessels serving as receivers, particularly independent receivers, ofelectric energy.

To insure a drop in voltage increasing with the current intensity inconsequence of the diaphragm, etc., constricting the cross section ofthe discharge it is advisable to keep its distance from the active anodesurface within certain limits. If this distance is too great, astriction cathode will form in the diaphragm opening and cause slowcathode radiation from the diaphragm opening to the inside of the spaceadjoining the active anode surface, but as long as the kinetic energy ofthis electronic radiation at collisions with the gas particles foundbetween the diaphragm and the anode can be fully utilized for formingnew pairs of ions, the drop in voltage in the portion of space betweenthe diaphragm and anode will not increase with the current intensityowing to the diaphragm. Only when the slow cathode radiation coming fromthe diaphragm impinges on the anode surface beforeit could fully utilizeits kinetic energy for the formation of new pairs of ions, i. e., whenthe reduced number of collisions between the soft cathode rays comingfrom the diaphragm and gas particles begins to limit the utilization ofthe kinetic energy ofthis radiation, will the drop in voltage betweenthe diaphragm and the anode increase with the'current intensity. It istherefore preferable to make the path of electronic radiation from thediaphragm or the like to the active anode surface not too long, andexperiments have shown that, at the highest, it should amount to a fewmean free lengths of path of electrons in the gas or vapor.

The back diffusion of neutral gas or vapor particles may further beimpeded by causing the discharge-from the diaphragm or the like to theanode surface to take place in a channel whose diameter is comparablewith that of the diaphragm and which terminates near the anode surface.The back difiusing particles are compelled by this arrangement to movefor several lengths of path inside a channel whose diameter is alsocomparable with the length of path. From the laws of the kinetic gastheory it is known that such a channel will increasinglyinterfere withthe free motion of the particles in proportion to its length. Thediaphragm opening lengthened by the channel extending to the anodesurface has, moreover, a particularly good effect according to theinvention, as the soft electronic radiation from. the diaphragm openingin the directionof the anode finds only a relatively narrow space for.collisions with neutral gas particles for forming new pairs of ions.

1 Instead of employing a single opening as F in Fig. 2 one may providea'plurality of diaphragm openings resembling a honeycomb or the squaresin a chessboard in the bottom of the body B, or, as indicated in Fig. 5,the bottom of the body B maybe formed by a porous member G in whichchannels are provided. In this case, several parallel discharges towardsone and the same anode A will takeplace simultaneously, which ispossible because each of these partial discharges has, according to theinvention, a positive voltage characteristic and thus can existsimultaneously in parallel connection with a discharge of the same kind.

As the high current density renders consider able heating at thediaphragm possible, it may be necessary to produce the diaphragm or thelike which constricts the cross section from a high melting material.

It will bedifiicult. as a rule, to cause ignition of the discharge fromthe anode A to the cathode K without a special exciter anode, since thediaphragm opening F brings about a'considerable increase in the sparkpotential. It is therefore advisable to arrange the diaphragm B or thelike which constricts the cross section of discharge in the form of aconductor which, as shown in Fig. 5, by a special current lead H and aresistance R. can be connected to the anode lead. When the anode takeson positive voltage values, a discharge between the diaphragm body B andthe cathode will firstignite. Owing to this discharge, a sufficientamount of electrons will be brought near the diaphragm openings, so thatthe voltage ofthe anode will sufiice to initiate the main dischargetowards the anode, which, once established, will continue to exist, evenif the current supply to the diaphragm B would be interrupted. Theresistance It may therefore be relatively high, so that after the anodeA has taken over the current conduction, only a relatively small currentor induction current flows through the diaphragm carrier B, theconductor H and the resistance R. The resistance B may of course beentirely disposed inside the discharge vessel to dispense with theconductor H. This is shown in Fig. 6 where the diaphragm body B providedwith a plurality of openings F is positioned directly on the anode A bymeans of an interposed member L of poorly conducting material, and theopenings F are elongated by the channels M and extend up toward theactive anode surface to prevent back difiusion of neutral gas or vaporparticles. The intermediate member L serves also for supporting themetallic diaphragm body B. It is possible to construct the body Bentirely from poorly conducting material and to position it on the anodeor its current-carrying conductor.

If a vessel is operated with alternating current, a drop in voltage willtake place, at least near the peak value of the current in the spaceadjoining the active anode surface. After the drop in voltage requiredfor initiating greater current intensities has been exceeded, thecurrent intensity will instantly increase to an amount correspondingtothe positive branch of the current-voltage characteristic and, if thisbranch rises relatively steeply, only an immaterial increase of theoperating current intensity will take place, so that the line diagram ofthe current intensity will have approximately rectangular shape.

The main feature of the invention is to successfully influence the dropin voltage of the tube by relatively simplein-built means near the.anode in such a way that it will increase in wholeor at least in partwith the current intensity so as to avoid series impedances whichcomplicate and increase the cost of the plant and involve additionallosses or a poor power factor. If the electric discharge vessel servesfor producing light, the diaphragm arranged near the anode surface maysimultaneously be used for producing the brightness of the discharge oran approximately point- 7713 and m represent the mass of the electronand positive ion. e=l.59 10 coulomb is the elementary charge. Formercury is For a discharge in mercury vapor the following formula willbe obtained wherein Ne refers to the number of positive charges whichpass through the screen opening of the cross section F, and J refers tothe strength of the discharging current.

Owing to the continual outflow of positive ions, a much higher vacuumwill be produced inside the chamber B than outside thereof. Assumed thatthe gas pressure is very low, e. g., 0.03 mm. mercury column, and thefree length of path of the gas particles comparable with the diameter ofthe opening F, this difierence in pressure can be calculated in a verysimple manner; it must be so great that the difference between thenumber of particles entering the chamber from outside and the numberleaving the chamber owing to the temperature motion is equal to thenumber of positive ions passed out by the current intensity. Accordingto the kinetic gas theory, a cross sectional area F will be passed pertime unit by a number of particles g 1/ HT 12 being the gas pressure inmm. mercury column and T the absolute temperature, and [.L the molecularweight of the gas. The excess particles, i. e., those entering thechamber in excess of the outflowing ones, are covered by this formula3.535.10 (P2-Pl) 02 al- 1/; F m

wherein m and T2 represent the pressure and the temperature outside thechamber and p1 and T1 the corresponding values inside the chamber. Formercury vapor =200 is assumed. If it is assumed that T1=T2=625 abs., thefollowing formula will result i. e., if in the cross sectional opening acurrent density of about 100 amps. per cm is assumed, it will result ina difierence in pressure amounting to 1/100 mm. mercury column betweenthe inside and outside of the anode chamber. This decrease in pressureis already so considerable that the electrons entering through theopening F to the inside of the anode chamber are no longer in a positionto form a sufiicient number of positive ions with the result that thenumber of the latter will decrease, as mentioned above. There will be anegative space charge and increased drop in voltage.

According to the simple physical laws involved, each current intensityand difference in pressure desired will correspond to a certain size ofthe cross-sectional opening, the exact ascertainment of which is lefttoexperiments. In an actually constructed tube the saturation currentintensity amounted to about 1 amp. at a temperature of the mercurycathode of about 17 C., a mercury vapor pressure of about 10- mm.mercury column and a diaphragm diameter of 5 mm.

If a gas discharge vessel according to the invention is operated withcurrent intensities near the point P (Fig. 1) where the characteristicchanges from an approximately horizontal to an approximately verticalcourse and if a series resistance to be found by testing or acorrespondingly dimensioned series choke DR (Fig. 7) are inserted in thecircuit, the tube will carry out slow oscillations, which is probablydue to the following causes:

A certain current intensity prevails at first under the influence ofwhich gradual evacuation of the chamber B is effected. When thisevacuation has reached a certain degree, this discharge will break, asinside the chamber the current and the voltage will rise, owing to thedecrease in the number of ions. When the current intensity decreases,the chamber will fill up with gas from the space E and the currentintensity can rise again. This process is repeated periodically. Thefrequency of the oscillations ranges from many seconds to fractions of asecond and can be regulated within these limits by the size of thechamber, the opening thereof, the gas pressure or the value of thesaturation current intensity depending on the gas pressure. In this wayit becomes possible to operate lamps working without outer elements,such as condensers, devices for an auxiliary discharge current, etc., ata predetermined interrupting frequency. Lamps of this kind may suitablybe used for advertising purposes, signal plants, etc.

I claim:--

1. An electric discharge vessel containing an ionizable medium undersufficiently high pressure to support a current discharge comprising atleast one anode, a cathode, a partition between the anode and thecathode dividing the discharge vessel into a smaller space directlyadjoining the active anode surface and a larger space, said partitionhaving an opening therein for passage of said discharge, the diameter ofsaid opening being of the magnitude of the mean free path of theparticles of the ionizable medium, whereby the discharge is constrictedat this point to a fraction of its cross section in the remainder of thespace and the current density is increased, the latter causing a paucityof ions and a potential drop corresponding to a current increase, and anauxiliary electrode adjacent the path of discharge provided with asuitable potential for controlling said discharge.

2. An electric discharge vessel containing an ionizable medium undersufliciently high pressure to support a current discharge comprising atleast one anode, a cathode, a partition between the anode and thecathode dividing the discharge vessel into a smaller space directlyadjoining the active anode surface and a larger space, said partitionhaving an opening therein for passage of said discharge, the diameter ofsaid opening being of the magnitude of the mean free path of theparticles of the ionizable medium, whereby the discharge is constrictedat this point to a fraction of its cross section, in the remainder ofthe space and the current density is increased, the latter causing apaucity of ions and a potential drop corresponding to a currentincrease, and two electrodes between said anode and said partition onopposite sides of the path of discharge for controlling its direction.

3. An electric discharge vessel containing an ionizable medium undersuiiiciently high pressure to support a current discharge comprising atleast one anode, a cathode, a partition between the anode and thecathode dividing the discharge vessel into a smaller space directlyadjoining the active anode surface and a larger space, said partitionhaving a plurality of openings therein for passage of the discharge, thediameter of said openings being of the magnitude of the mean free pathof the particles of the ionizable medium, whereby the discharge isconstricted at this point to a fraction of its cross section in theremainder of the space and the current density is increased, the lattercausing a paucity of ions and a potential drop corresponding to acurrent increase, and an auxiliary electrode-system provided with asuitable potential adjacent the path of discharge for controlling saiddischarge. 7

4. An electric discharge vessel containing an ionizable medium,comprising an anode, a cathode, a partition of conducting materialbetween the anode and a cathode dividing the vessel into a smaller spacedirectly adjoining the active surface and a larger space, said partitionbeing connected with the anode by a resistance outside the vessel, saidpartition having an opening therein, the diameter of the opening beingof the magnitude of the mean free path of the particles of the ionizablecontent, said structure causing a paucity of ions and a potential dropcorresponding to a current increase, and an auxiliary electrode-systemprovided with a suitable potential adjacent the path of discharge forcontrolling said discharge.

WAL'IER \DALLENBACH.

